The label associated with the acronym can only be ASCII. The acronym itself can be anything supported by LaTeX. Your link mentions: "You can define acronyms with \acrodef{label}[acronym]{written out form}, for example \acrodef{etacar}[$\eta$ Car]{Eta Carinae}, with the restriction that the label should be simple ASCII." Note the use of math mode $..$ in the acronym. Do you want \textsc as the default for all your acronyms or just some?
–
WernerDec 8 '11 at 20:01

For me it is ok to set something like \acrodef{API}[\textsc{API}]{Application Programming Interface} but it is not working as expected and what I get is the usual plain text.
–
mariosangiorgioDec 8 '11 at 20:58

Nevermind, I tried it again and it worked. It just required an additional compilation.
–
mariosangiorgioDec 8 '11 at 20:59